How much time do you need to spend with your children?

Here's a great mathematical answer I found on a homeschooling website.

"When a baby is born, before he's a year old, spend 23 hours a day with him, or thinking about him, or sleeping with him, or carrying, or feeding him.

When he turns one, spend 22 hours a day with him (and gradually less). For two hours you might be in the shower or sleeping without knowing you're asleep.

Let that time slide at a steady pace until he's ten or eleven, and you're spending half of it, twelve hours, with him, on him, in his presence, doing things for or with him. Steadily slide that back until he's 20 and then one hour a day is plenty.

No cheating. If you aren't diligent in the early years, the 20 year old will be gone in a huff or might have slunk away sadly."